Obsidian-Hydration Dating, the Coner Phase, and Revisionist Chronology at Copan, Honduras

Abstract

The technique of obsidian-hydration dating contains great potentials for error, from both laboratory determinations of rate constants and measurements of effective hydration temperatures (EHTs) in the field. The rate constants used to determine these dates are of questionable validity and need to be independently verified. Significantly, no measurements of EHTs were taken at the site of Copán, Honduras, until the majority of the obsidianhydration dates were calculated. An error of but a few Kelvins in estimated EHT can lead to dates that are in error by several centuries. In view of the likelihood of large errors in the Copán obsidian dates, the assertion that the Late Classic Coner phase should be extended beyond A. D. 900 (Webster and Freter 1990a) is premature.